This 1984 info is obsolete of course as the 1991 Lemans
engine was entirely different. The next three charts are
for the Lemans engine config. The pipe lengths shown here
are in addition to the fixed length of around 17 inches.
The diameters of the pipe are around two inches.
We came pretty close to duplicating the Lemans p-port engine
results with a Weber carb on the Mazdatrix dyno.
Torque peak is not only a function of pipe length
but also a function of diameter as shown in the least chart.
Perhaps something to due with Helmholtz theory.
Paul Lamar ...No rotor no motor.
Paul,
Can you explain the short intake runner length numbers here with the
dyno data you provided earlier concerning the Weber 58mm carburetor-
they seemed to imply that longer runners, between 24" and 28", are
preferred for operations near 6000 rpm, not the 14" used here?
One more question: Im leaning towards using a throttle body, but,
assuming 4 long runner tubes, as for a 4-port Renesis intake design, do
you feel your slide throttle still a viable option or will it be too
long physically? Any thoughts to an engine-perpendicular moving slide
orientation instead of parallel to the engine?
Mike Parker
My best guess is it was a much smaller engine (2 L) than the 13B
(2.6 L) so the runner diameter was probably much smaller. According
to this chart the smaller the runner the lower the torque peak so
to move the torque peak back up one must shorten the runner.
This is not to say the torque is optimized. If the torque is
NOT optimized at a given RPM then so too is the HP NOT optimized.
Small pipes have higher skin friction drag than large pipes
for a given volume flow rate.
I have always considered that chart apparently contradictory and I
rarely upload it for that reasons. I am impressed you noticed the
difference :) I would not be a bit surprised if the engineers at
Mazda in 1984 were unaware of the runner diameter effects on the
torque peak RPM. I could be wrong. This chart was published in 1995
in Advanced Engine Technology by H. Heisler. In the classic
book Scientific Design of Exhaust & Intake Systems by P.H. Smith
& J.C. Morrison, first published in 1961, third edition 1971,
IMHO this effect was not noted. Only length was considered.
However by 1991 and the Lemans engine with 13B width rotors
Mazda engineers had finally gone to about as large a pipe diameter
they could given the width of the rotor housings and the need for
support for the apex seal as it passed over the p-port hole. No
one to my knowledge every got more NA HP at any given RPM than the
Lemans engines. Perhaps Racing Beat or Guru but Jim never published
any HP curves for his NA p-port engines that I could find.
The 16b p-port engine will be a sight to behold with 2.5 inch
runners possible with 50% more port area than the 13B's two inch.
My guess max NA HP for a p-port 16B two rotor will be in the
range of 375 to 400 HP at 9000 RPM with an unprecedented
power to weight ratio.
With four runners, say 2 inches in diameter, a slide throttle
will be much longer.
Slide throttles work best with a p-port. Since there
apparently is a huge penalty for making the air turn 90
degrees through side ports I would not bother with side
ports for an aircraft engine. Everett Hatch and Allan Tolle
proved that ten years ago with 238 MPH in the Sun 100 race
and the all time fastest time to climb from a dead stop
on the runway to 3000 feet including jet fighter planes.
Unfortunately the spur gear box was not up to it and failed.
Intake systems are aerodynamic devices. The lower the aero drag
the lower the pumping losses, the higher the HP and the better
the BSFC in our RPM ranges. Lower RPM ranges (less than about
3500 RPM) misfiring occurs due to high passage area overlap in
P-ports destroying the BSFC, average torque and HP. That is the
reason the RX8 engine has both side intake and side exhaust. It
cuts the over lap passage area.
Paul Lamar ...No rotor no motor.
Ops forgot to attach the chart.
Paul Lamar ...No rotor no motor.
Paul,
I have always found these charts very confusing.
Is there any way an experiment could be done on tube ID size, tube length,
inlet speed and volumetric efficiency, in a way where the manifold isn't
attached to the engine - like some sort of flow tester?
George (down under)
If you have four pipe diameters and four lengths to try you need
to make sixteen test rigs :)
Or you could make four variable length pipes of different diameter.
Close one end and blow air over the air end. They will act like
organ pipes. Use a audio program on the PC that gives you the frequency
and amplitude of the sixteen different tones.
Reminds me of this story :) I am sure many of you have seen it
on the Internet but here it is again.
----------------------------------------------
Sir Ernest Rutherford, President of the Royal Academy,
and recipient of the Nobel Prize in Physics, related
the following story:
"Some time ago I received a call from a colleague.
He was about to give a student a zero for his answer
to a physics question, while the student claimed a
perfect score.
The instructor and the student agreed to an impartial
arbiter, and I was selected.
I read the examination question: "Show how it is
possible to determine the height of a tall building
with the aid of a barometer."
The student answered: "Take the barometer to the top
of the building, attach a long rope to it, lower it
to the street, and then bring it up, measuring the
length of the rope. The length of the rope is the
height of the building."
The student really had a strong case for full credit
since he had really answered the question completely
and correctly.
On the other hand, if full credit were given, it could
well contribute to a high grade in his physics course
and certify competence in physics, but the answer did
not confirm this.
I suggested that the student have another try.
I gave the student six minutes to answer the question
with the warning that the answer should show some
knowledge of physics.
At the end of five minutes, he hadn't written anything.
I asked if he wished to give up, but he said he had
many answers to this problem...he was just thinking
of the best one.
I excused myself for interrupting him and asked him
to please go on.
In the next minute, he dashed off his answer,
which read:
"Take the barometer to the top of the building and
lean over the edge of the roof. Drop the barometer,
timing its fall with a stopwatch. Then, using the
formula x=0.5*a*t^2, calculate the height of the
building."
At this point, I asked my colleague if he would
give up. He conceded, and gave the student almost
full credit.
While leaving my colleague's office, I recalled
that the student had said that he had other answers
to the problem, so I asked him what they were.
"Well," said the student, "there are many ways of
getting the height of a tall building with the aid
of a barometer.
For example, you could take the barometer out on a
sunny day and measure the height of the barometer,
the length of its shadow, and the length of the
shadow of the building, and by the use of simple
proportion, determine the height of the building."
"Fine," I said, "and others?"
"Yes," said the student, "there is a very basic
measurement method you will like. In this method,
you take the barometer and begin to walk up the
stairs. As you climb the stairs, you mark off
the length of the barometer along the wall. You
then count the number of marks, and this will give
you the height of the building in barometer units."
"A very direct method."
"Of course. If you want a more sophisticated method,
you can tie the barometer to the end of a string,
swing it as a pendulum, and determine the value of
"g" (gravity) at the street level and at the top of
the building. From the difference between the two
values of g, the height of the building, in principle,
can be calculated."
"On this same tack, you could take the barometer to
the top of the building, attach a long rope to it,
lower it to just above the street, and then swing it
as a pendulum. You could then calculate the height
of the building by the period of the precession".
"Finally," he concluded, "there are many other ways
of solving the problem.
Probably the best," he said, "is to take the barometer
to the basement and knock on the superintendent's door.
When the superintendent answers, you speak to him as
follows: 'Mr. Superintendent, here is a fine barometer.
If you will tell me the height of the building, I will
give you this barometer."
At this point, I asked the student if he really did
not know the conventional answer to this question.
He admitted that he did, but said that he was fed up
with high school and college instructors trying to
teach him how to think.
--------------
The name of the student was Niels Bohr(1885-1962)
Danish Physicist; Nobel Prize 1922; best known for
proposing the first 'model' of the atom with protons
and neutrons, and various energy states of the
surrounding electrons -- the familiar icon of the
small nucleus circled by three elliptical orbits,
more significantly, an innovator in Quantum Theory.
-------------------------------------------------
Paul Lamar ...No rotor no motor.
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